Brad Pitt, who was a big fan of Arnaques, crimes et botanique (1998), approached director Guy Ritchie and asked for a role in this film, as he wanted to move away from commercial movies and work with new directors. Reportedly, Ritchie originally wanted Pitt to play Turkish, but when he found out that Pitt couldn't master a London accent, he created the role of Mickey the Pikey for him, and the role of Turkish went to Jason Statham.
There are several stories behind Brad Pitt's character Mickey and his indecipherable speech. One states that it was inspired by many critics' complaints about the accents of the characters in Guy Ritchie's previous film Arnaques, crimes et botanique (1998). Ritchie then decided to counter the criticisms by creating a character that was not only unintelligible for the audience, but couldn't be understood by characters in the movie either. Other sources state that it was Pitt's own attempt to get back at Irish viewers and critics who had ridiculed his Irish accent in Ennemis rapprochés (1997). Ritchie himself has stated that he made Pitt an Irish Traveler because Pitt couldn't do a London accent, but his Irish one was passable. The director also thought it would be funny to cast one of Hollywood's best paid stars and two-time People Magazine's Sexiest Man Alive in the film, and make him as ugly and incomprehensible as possible. Finally, Pitt himself admitted that the day before shooting was to commence, he got cold feet because he couldn't make his Traveler dialect work. He contacted Ritchie, asking him to be released from the part and persuading Ritchie to play the part himself. Ritchie refused, so Pitt asked a crew member he had befriended for advice, who told him that it didn't matter what he did, as no one understands British gypsies anyway. This gave Pitt the idea to make Mickey completely unintelligible, to which Ritchie agreed.
When Guy Ritchie told Brad Pitt that he would be playing a boxer, Pitt became concerned because he had just finished shooting Fight Club (1999) and did not want to play the same type of role again. Pitt took the role anyway because he wanted to work with Ritchie so badly.
Every mistake that Sol, Vincent and Tyrone make were inspired by various late-night TV shows about real-life crimes gone horribly wrong.
When Vinny and Sol are sitting outside Brick-Top's Bookies, about to give him the diamond, the man that approaches the car is not really Bullet-Tooth Tony, it was a look-alike. Vinnie Jones didn't show up for shooting that day because he was in jail for fighting the night before.
Guy Ritchie: In the back of the bar when we are first introduced to Doug The Head. Ritchie is the man reading the newspaper.